Not Just Another 7 vs 9 Thread

[N941WR]

Originally Posted by StuBob

...
So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?
...

The -9 is more balanced in its control harmony than the -7.

That is just one reason.

[Raymo]

Originally Posted by StuBob

The mission: Fly from the Midwest to Alaska and back in an airplane you built yourself.

The first considerations: What airplane, RV7 vs RV9, nose wheel vs tailwheel, c/s vs fixed, carbureted vs injected? If it weren't for Vlad, everyone would say 7 for fuel capacity, c/s for takeoff performance, injected for LOP, and tailwheel for gravel runways. But Vlad is inspiring!

Assume 180hp RV7 or 160hp RV9, no interest in aerobatics, and no interest in aftermarket fuel mods.

Are you planning to build or buy? If buying, I suspect you'll find a -9(A) faster than a -7(A). Either will serve your mission well. The rest is likely nit-picking around the fringes of your mission scope (short field, O2 at high altitudes).

When I was looking for a used kit, everything was on the table but I found a great deal on a -7A first. If I'd found a similar deal on a -9 first, I'd be flying it and be just as happy. I enjoy doing rolls and look forward to loops but that ability was not critical to my decision making.

One advantage not mentioned about an A model is lower insurance cost. The tail-wheel folks (no offense intended) never seem to compare the number of ground loops with the number of nose gears that folded

[StuBob]

It’s a motivator to get me stay in the garage.

[PerfTech]

Originally Posted by StuBob

This thread, combined with further research here, other sites, Van's, etc., brings me to this summary, as relates to the 3000nm AK trip. Assume two airplanes built per Van's recommendations, i.e., 160hp RV9 and 180hp RV7:

1) 100 mi range advantage 7.
2) 100 ft takeoff/landing distance advantage 9.
3) Cruise speed 10+ knots advantage 7.
4) 8 mph stall speed advantage 9.
5) The prices are almost identical, subject to prop choice.

So the 9, with 20hp less, costs the same as the 7. What does the 9 give back in return for that 20ph?

Because I'm a contrarian, I really want to prefer the 9 taildragger. But this morning's math is providing a hurdle.

... I think there are a few things in this thread that were overlooked and possibly could be misconstrued by some. I see these numbers thrown out from Van's website for comparison purposes, and no one has mentioned (or I missed it) the fact that the RV-7 numbers on Van's site were gathered with a C/S prop, and the RV-9 numbers were with a F/P. This really changes the game as in take off and landing distances for one, as well as climb. I have a C/S on my 9 and believe me that is a real game changer. I routinely fly off a 500 ft. strip with obstacles at gross, and have yet to see that from another model. Also comparing the two aircraft at 8000' where the 7s perform there best isn't exactly apples with apples. My 9-A cruises @ 207 tas. on 7.1 gph. @8000', when up where I usually cruise 14,500 the fuel burn drops to less than 6.5 gph. with no reduction in tas. This reduction also considerably extends the range to five hrs. with reserve, (about 1,000 miles). Another thing I really like with the 9 series is the rock solid feel at higher altitudes. I fly high (16,500) when winds favor it, and the 9 doesn't even begin to drop its tail and mooch around like models designed to fly at lower altitudes. To me, for what I do the 9s are the best I have seen! The 7s in all fairness do have some advantages, as in aero rating, will fit in a smaller hangar, easier to wash, cheaper to paint, and the #7 just sounds lucky...

[StuBob]

Allan, what engine are you using to get that TAS?

[PerfTech]

Originally Posted by StuBob

Allan, what engine are you using to get that TAS?

....160 HP 320. I do run my rpm up higher, as my prop is modified to work better at the higher rpm. This will allow the engine to make a few more horses. I have also paid a lot of attention to eliminating as much aero drag as possible, as well as some rigging changes etc. Thanks, Allan..

[tomww]

Originally Posted by PerfTech

... I think there are a few things in this thread that were overlooked and consequently misrepresented. I see these numbers thrown out from Van's website for comparison purposes, and no one has mentioned (or I missed it) the fact that the RV-7 numbers on Van's site were gathered with a C/S prop, and the RV-9 numbers were with a F/P. This really changes the game as in take off and landing distances for one, as well as climb. I have a C/S on my 9 and believe me that is a real game changer. I routinely fly off a 500 ft. strip with obstacles at gross, and have yet to see that from another model. Also comparing the two aircraft at 8000' where the 7s perform there best isn't exactly apples with apples. Me 9-A cruises @ 207 tas. on 7.1 gph. @8000', when up where I usually cruise 14,500 the fuel burn drops to less than 6.5 gph. with no reduction in tas. This reduction also considerably extends the range. Another thing I really like with the 9 series is the rock solid feel at higher altitudes. I fly high (16,500) when winds favor it, and the 9 doesn't even begin to drop its tail and mooch around like models designed to fly at lower altitudes. To me, for what I do the 9s are the best I have seen! The 7s in all fairness do have some advantages, as in aero rating, will fit in a smaller hangar, easier to wash, cheaper to paint, and the #7 just sounds lucky...

Interesting idea that something can be overlooked and thus misrepresented.

One of the strengths of the 9, IMHO, is the lower stall speed and all that implies.

But you won’t find me ignoring the advice from Vans is it? A A pilot of an RV- 9A who is exceeding structural cruise speed, no matter how carefully and skillfully he flies, is not in control of the critical factors and is putting himself and his passengers at risk.

Have a look at the advice on engine size before pushing the limits. If you are going into that territory you might be much safer in the 7 due to its extra strength. If you choose to fly close to VNE I hope your guardian angle or whoever looks after you is looking out for you.

[N941WR]

Originally Posted by tomww

...
But you won’t find me ignoring the advice from Vans is it? A A pilot of an RV- 9A who is exceeding structural cruise speed, no matter how carefully and skillfully he flies, is not in control of the critical factors and is putting himself and his passengers at risk.
...

207 mph TAS is not beyond the Vne of 210 mph TAS. It is close, very very close.

Allan must have some tricks up his sleeve because my O-360 powered -9 tail dragger will hit the wall right at 200 MPH / 175 knots, which is just fine by me.

His comments about flying high are right on the mark. Even at 17.5 the -9 is still flying nose down. Whereas the short wing RV's are flying nose up at those altitudes.

[ChiefPilot]

Originally Posted by N941WR

207 mph TAS is not beyond the Vne of 210 mph TAS. It is close, very very close.

Tom wasn't referencing Vne. Max structural cruise speed, Vno, is something different.

[ChiefPilot]

Originally Posted by N941WR

Even at 17.5 the -9 is still flying nose down.

The picture you posted earlier in this thread, in post #8, shows this to be false.